"Most present with erectile dysfunction," says Dr. Ronald W. Raspa, a urologist with Middletown Urologic Associates, who then asks about energy levels and whether a patient is feeling sad or grumpy. "You should still have a zest for life even as you age. Maybe you pursue these interests a little less vigorously ... but if a general physical indicates there are no underlying problems, then test for low testosterone."

Testosterone is the primary male hormone responsible for growth and development at puberty, says Hines. It is the pea-size pituitary gland at the base of the skull, however, that tells the testicles how much testosterone to produce. That message is delivered by hormones known as LH and FSH.

"Studies indicate that after the age of 25 or 30, testosterone levels decrease about a half a percent a year," he says. "But before the age of 60, the levels still usually fall well within the normal range."

Because testosterone is involved in the sleep-wake cycle, levels are typically at their peak between 6 and 8 a.m.

"'Low' is under 300 in a man younger than 60," says Hines. "I'm seeing more and more referrals for low T checked at 2 p.m. Before I consider treatment, I want to see two low levels at 8 a.m. This is the recommendation from the Endocrine Society."

Raspa also checks for free testosterone levels, or the small amount of testosterone in the bloodstream that is not bound to other chemicals, which can provide an additional window to overall health.

"Morning testosterone is the highest, but if a patient is borderline low and fits the profile, we'll talk about treatment. If the testosterone makes a difference, great; if he feels the same as he did before, then we won't continue.

"In the course of treating, I've had men tell me they used to be sad, but now they feel better; they're no longer tired and depressed. Testosterone supplementation may not cure ED, but it can have independent effects."

So why might treatment not work?

Because testosterone is necessary for reproduction, low testosterone levels are sometimes thought to be an evolutionary side effect that prevents a sick organism from reproducing.

"So it's important to first rule out other causes," says Hines.

Many diseases, the experts says, such as cancer, COPD, diabetes and declining organ function, vascular disease, particularly with increased cholesterol, and even sleep apnea will result in low testosterone levels, also called hypogonadism. There might also be an abnormality of the pituitary gland or damage to the testicle rendering it unable to respond.

"Oftentimes if you treat the underlying condition, testosterone levels will go back to normal," says Hines.

However, if everything else checks out and the primary problem is, in fact, low testosterone levels, there are several treatment options.

-- Topical preparations such as gels, foams or a patch. While they're noninvasive and provide a relatively constant level, it takes time to absorb. With a gel, there can't be bodily contact with a female without a shower (unless the gel is applied, say, under the arm). Patches can cause reddening of the skin.

-- Injections. A larger needle is required because of the viscous property of the testosterone, so the shot is delivered to the buttocks or thigh. It lasts about two to three weeks, and the level fluctuates.

-- Implants. Only a urologist can implant testosterone pellets under the skin. Raspa says this is his preferred method of treatment. Ten tiny testosterone pellets are implanted in the fatty tissue of the buttock. They dissolve slowly and release a gentle, sustained level of the hormone, which lasts for four to six months. The timing of subsequent implants is adjusted during follow-up visits.

Regular monitoring is a critical component of testosterone supplementation because of potential side effects.

"Too much T can lead to 'roid rage,'" says Hines, referring to the abuse of steroids by some athletes who want to increase muscle mass and strength. Because of that, testosterone is treated like a narcotic. A monthly prescription is required — and there are no refills.

Too much testosterone can also result in infertility, he says, by causing a drop in the pituitary messengers LH and FSH, which are also needed for sperm production.

"One discussion I'll always have with a man is whether he's through with wanting children, as we can be potentially affecting LH and FSH," says Hines.

Hines and Raspa also caution that too much testosterone can increase the number of red blood cells. "Too many, and the blood becomes viscous," says Hines.

This can result in clots ending up in the lungs or brain, says Raspa — requiring routine tests of not only testosterone levels, but also blood counts.

"Too much testosterone can also cause an inflammation of the hepatic cells and liver damage," says Hines.

"It's usually reversible, but it has to be checked," says Raspa.

And although testosterone doesn't cause prostate cancer, the experts agree, it can make it worse.

"If a man has a small prostate cancer, (testosterone supplementation) can cause the cancer to grow rapidly," says Hines. "A digital rectal exam and PSA test need to be done beforehand."

So not unlike questions to be considered with estrogen supplementation in a woman, potential cardiac and cancer risks need to be weighed against other concerns — including an increased risk for bone fractures. As in postmenopausal estrogen decline, men with low testosterone run the risk of thinning bones.

"If you're older than 60, testosterone levels will be lower over time. Are there physiologic reasons not to mess around?" says Hines. "There's still a lot of unknowns, and experts do not agree whether testosterone replacement is truly beneficial for men over the age of 60. This is why it's so important for physicians to discuss the potential risks and benefits with patients so that each individual patient can decide whether they want to consider treatment."

"It's safe to supplement in most circumstances," says Raspa. "We used to think the effects of aging were natural. Now we know we can cheat a little to keep our youthful vigor."